Temperature regulation of air heaters



Jan. 15, 1952 C- F- HAWLEY 2,582,830

TEMPERATURE REGULATION OF AIR HEATERS Filed Jan. 2l, 1946 CHARLES 1F. /A WLEY www Patented Jan. 15, 1952 TERIPERATURE REGULATION OF AIR HEATERS Charles F. Hawley, Holden, Mass., assgnor to Riley Stoker Corporation, Worcester, Mass., a corporation of Massachusetts Application January 21, 1946, Serial No. 642,451

4 Claims. l A This invention relates to vapor generators, and more particularly to vapor generators of the type having a combustion chamber or furnace fired with pulverized fuel, the fuel being burned in suspension. v

In such apparatus it is a common practice to provide a pulverizer to prepare the fuel, which is conveyed to the furnace by a current of socalled primary air. Additional or so-called secondary air is supplied to the furnace at the rate required to complete the combustion of the fuel. It is also customary to utilize the flue gases which leave the heating surfaces of the vapor generator to raise the temperature of an air stream, and to use this air stream to supply bot the primary air and the secondary air requirements. The heated secondary air improves the combustion conditions,-and the heated primary air is of great assistance in drying the fuel and in facilitating the pulverization thereof.

In installations which burn fuels of unusually high moisture content, the prior arrangements are not entirely satisfactory. In such installations it is desirable to heat the primary air to considerably higher temperatures than the secondary air. Furthermore, in the case of steam generators operating at comparatively low pres` sures the flue gases are relatively cool, and it ,may be desirable to heat the primary air to a temperature exceeding the normal temperature of the ue gases. This is not possible with apparatus as ordinarily constructed heretofore.

it is accordingly one object of the present invention to provide a vapor generator fired with pulverized fuel and particularly adapted for operation with high moisture fuel.

It is a further object ofthe invention to provide a steam generator fired with pulverized fuel and capable of operating satisfactorily with high moisture fuel even when generating steam at relatively low pressures.

With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth Kin the specification and covered by the claims appended hereto.

Referring to the drawings illustrating one ernbodiment of the invention, and in which like reference numerals indicate like parts, the single figure is a vertical longitudinal section through a steam vgenerator arranged for pulverized fuel lfiring.

rFhe embodiment illustrated comprises a transfverse steam-and-Water drum Ill, a transverse 'fwater drum- II therebeneath, anda bank of upright water tubes I2 connecting the drums. A row of water tubes I4 extendsl upwardly from the front portion of the lower drum il and then forwardly to a small transverse drum or header I5. Water tubes I6 extend rearwardly from the front drum I5 to the steam-and-water drum I0, these tubes serving to support the roof I'l of the boiler setting. A furnace or combustion chamber I9 is located in front of the lower drum I I, this furnace having a front wall 23 extending upwardly to the front drum I5, a rear wall 2| extending upwardly to the lower drum II, and two side walls 22 (one only being shown). Water wall tubes 2li are associated with the front wall 20 and are connected at their upper ends to the front drum I5. Water wall tubes 25 are associated with the rear wall 2 I, and the upper portions of these tubes are bent forwardly to connect with the front drum I5. A suitable pulverizer 2'I delivers pulverized fuel through a pipe 28 to a burner 29 mounted adjacent an opening 30 in the front wall 20.

The gaseous products of combustion from the furnace I9 are guided in a proper course through the boiler by means of suitable baiiles. As shown, a baille 32 extends upwardly from the lower drum I I along the tubes I4 to direct the gases upwardly between the front portions of the tubes Ill and v25, adjacent the front drum I5. A baiile 33 eX- tends downwardly from the steam-and-water drum Il] along the front portion of the tube bank I2, so that the gases are directed downwardly between the baffles 32 and 33 and into the lower portion of the tube bank. An upright baie 34 is located directly behind the tube bank to co.- operate with the baffle 33 in defining a passage through which the gases may ow upwardly in contact with the tubes I2 and thence into a passage 35.

Somewhat above and to the rear of the steamand-water drum Iii there is provided a primary air heater comprising a casing 3l, a front bank of upright tubes 33 extending through the casing, and a rear bank of upright tubes 3Q extending through the casing. The gas passage 35 ,leads directly to the lower ends of the front tubes 38. At the top of the casing 3i' there is provided a box 4I which serves to direct the gases from the upper ends of the front tubes 38 into the upper ends of the rear tubes 39. After flowing downwardlythrough the rear tubes, the gases enter a passage 42 behind the passage 35. The casing 31 has an air inlet 44, an air outlet l5 and two staggered horizontal baiiies it to direct air in three passes across the tubes 33 and 39. The outlet 45 is connected by `a duct 41 to the Iuel pulverizer 21. Beneath the primary air heater 3i there is provided a secondary air heater` comprising a casing 49 through which there extends a bank of vertical tubes 59 with their upper ends in communication with the passage 42 and their lower ends in communication with a passage 5I. This passage 5I may lead to an induced draft fan or stack (not shown). Air is delivered to the lower end of the casing 49 by a forced draft fan 53, and the heated air may escape from the upper end of the casing 49 to the burner 29 through. duct 54 provided with a damper 55. Heated air may also escape from the upper end of the cas; ing 49 through a duct 51 provided with a damper 58 and leading to a fan 59, the latter serving to discharge the air through the: inlet 4d of the primary air heater.

In some installations utilizing high moisture fuel, and particularly with steam generators operating at low pressures, the ilue gases which have traveledv upwardly vin contact with the' water tubes I2 may be at a temperature lower than that which is desirable for the primary air. `In order that the primary air may be heated sufciently, means is provided to by-pass a controlled portion of the flue gases, out of contact with the water tubes. For this purpose the secondary air heater casing 49 is spaced rearwardly from the baiile 34 to provide a vertical passage 6I connected at its upper end with the passage 35. Gases may enter the lbwer end of the passage 6I by owing rearwardly directly across the lower portions of the Water tubes I2 and beneath the lower edge of the baffle 34, which is spaced from the water drum I I. A hopper 52 is provided be'- hind the drum II to collect any ily-ash which is discharged from the` gases as they enter the passage 6I. Dampers '6'4 and 65 are provided in the lower portion of the passage 35 and located respectively behind and in front of the baille 34, to control the proportionate ow of gases on opposite sides of this baiie.

The operation of the invention will now be ap'- parent from the above disclosure. Fuel and air will enter the furnace I9 through the opening 39, and combustion will take place, the gaseous products of combustion owing upwardly across the front portions of the water tubes I4 and 25 and then rearwardly and downwardly between the battles 32 and 33 to the lower portion of the water tube bank I2. Here the gases will divide in accordance with the relative adjustments of the dampers 84 and 65, a portion of the gases flowing upwardly in contact with the tubes I2 between the baiiles 33 and 34 to enter the passage 35, and the remainder 'owing upwardly through the by-pass 6I to enter the passage 35 and there mix with the rst portion. Since the gases in the passage 6I have by-passed most of the heati absorbing surface of the Water tubes I2, these gases will be considerably hotter than the gases which flow upwardly in front of the baille 34. Consequently the dampers 64V and 65 provide a means for varying the temperature ofthe mixed:

Steam will be gen-v the casing 49, and this air will flow upwardly in contact with the tubes 50 and thus be heated in a desired manner. From the upper end of the casing 49 a part of the heated air will travel through the duct 54 to the burner 29, under control of the damper 55, and enter the furnace as secondary air for combustion purposes. The remainder of' the heated air will ow past the damper 58 and through the duct 51 to the fan 59 and thence into the casing 31. This air will travel around the baiiies 49, making three passes across the tubes 38 and 39, and then through the duct 41 to the pulverizer 21, where it will serve 'as primary air to dry the fuel and convey the same through the pipes 28 to the burner 29.

By adjustment f the dampers 64 and 65 the temperature4 of the mixed gases in the passage 35 may be varied as desired, and in this manner the temperature of the primary air entering the duct 41 may be controlled. If necessary, for example when burning very Wet fuels, the primary air temperature can be made to exceed the temperature of the flue gases approachingV the damper B5. The primary air fan 59 renders it unnecessary to maintain sucient pressure in the secondary air supply to overcome the resistance of the primary air heater. Thus the load on the secondary air' fan 53 may be appreciably decreased.

Having thus described my invention, what I claim as new and desire lto secure by Letters Patent is:

l. A vapor generator comprising liquid-containing elements, a primary air heater, a secondary air heater, means to supply air to the secondary air heater to be heated thereby, means to conduct part of the heated air from the secondary air heater to the primary air heater to be heated thereby, a passage through which hot gases may ow in contact with the said liquidcontaining elements and thus be appreciably reduced in temperature, a by-pass for said passage through which hot gases may flow and be dis'- charged at a temperature appreciably exceeding the temperature of the gases leaving the said passage, means to control the relative rates of gas iiow in the passage and the by-pass, means to conduct all the gases from both the passage and the by-pass directly to the primary air heater, and means' to conduct the gases from the primary air heater to the secondaryv air heater.

2. A vapor generator comprising a bank of substantially parallel liquid-containing tubes, a primary air heater', a secondary air heater, means to supply air to the secondaryy air heater to be heated thereby, means to conduct part of the heated air fromI the secondary air heater to the primary air heaterV to be heated thereby', a passage through which hot gases may flow along the tube bank in contact with the tubes and thus be appreciably reduced in temperature, a bypass for the passage which hot gases4 may enter by flowing directly across one end of the tube bank without appreciable reduction in temperature", means to control the relative rates of gas flow in the passage and the by-pass, means to conduct all the gases from both the passages and the by-p'ass directly to the primary air heater, and means to conduct the gases from the primary air heater to the secondary air heater.

3. A vapor generator comprising a bank of upright liquid-containing tubes, a primary air heater, 'a secondary air heater, means to supply 'air to the 'secondary' 'air heater to` be Heated thereby, means to conduct part of the heated air from the secondary air heater to the primary air heater to be heated thereby, means to deliver hot gases to the tube bank adjacent one end thereof, a passage through which a portion of the hot gases may flow along the tube bank in contact with the tubes and thus be appreciably reduced in temperature, a by-pass for the passage which a portion of the hot gases may enter by owing directly across the said end of the tube bank Without appreciable reduction in temperature, means to control the relative rates of gas ow in the passage and the by-pass, means to conduct all the gases from both the passage and the by-pass directly to the primary air heater, and means to conduct the gases from the primary air heater to the secondary air heater.

4. A vapor generator comprising a bank of upright liquid-containing tubes, a primary air heater, a secondary air heater, means to supply air to the secondary air heater to be heated thereby, means to conduct part of the heated air from the secondary air heater to the primary air heater to be heated thereby, means to deliver hot gases to the tube bank adjacent the lower end thereof, a passage through which a portion of the hot gases may ow upwardly along the tube bank in contact with the tubes and thus be appreciably reduced in temperature, a by-pass for the passage which a portion of the hot gases may enter by flowing directly across the lower end of the tube bank without appreciable reduction in temperature, means to control the relative rates of gas ow in the passage and the by-pass, means to conduct all the gases from both the passage and the by-pass directly to the primary air heater, and means to conduct the gases from the primary air heater to the secondary air heater.

CHARLES F. HAWLEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,243,913 Marshall June 3, 1941 2,386,188 Artsay Oct. 9, 1945 2,396,102 Jackson et al Mar. 5, 1946 OTHER REFERENCES Pub. (Heat Engineering, June 1942, No. 6, vol. XVII, pages 74 and 75).

Pub. (Heat Engineering, June 1942, No. 6, vol. XVII, page 76). 

